A new approach to vector surveillance is proposed. Mosquitoes of both sexes are attracted to particular nectar-bearing plants that generate volatile chemicals. Preliminary experiments demonstrate that mosquitoes orient to these mixtures, and that they can be used as lures to trap large numbers. Yet virtually nothing is known of their composition, and their use in surveillance traps has never been explored. As widespread early-warning and sampling devices, these attractants have advantages over those currently available or being developed, most of which are based on kairomones from vertebrate hosts. The latter attract only females and only those that have entered the blood-feeding mode. Plant derived attractants, on the other hand, a) attract mosquitoes as early as 1 day after emergence, b) attract early-emerging, localized males, as well as pre- and post-dispersal females, c) attract females in all gonotrophic states, d) attract females in reproductive diapause, and e) can be slow-released in tiny amounts over extended periods. Therefore, phytochemicals provide earlier and more precise information on mosquito mass emergences and population composition, and they can be deployed in simple, lightweight traps. The proposed project has two objectives: 1) to create the most attractive synthetic blends of component volatiles of the plants most frequently used as sources of sugar by two of the most important mosquito species in the U.S.; 2) to determine the most effective blend and its release rate in traps that can be used in surveillance of these species. The targets are Aedes vexans, considered the most important biting pest in the Midwest and elsewhere, and Culex pipiens, the presumptive primary vector of West Nile virus in the northeastern quadrant of the U.S. The procedure will be a 4-step process: a) analyze the components of floral headspace, b) assay the relative bioactivity of fractions and synthetic blends by mosquito olfactometer, c) test the most attractive blends in the field at a series of release rates, using MM-X olfaction traps, and d) compare phytochemical-based and vertebrate kairomone-based traps simultaneously over extended periods, while sampling the local resting population with a power aspirator, to evaluate their relative performance as surveillance and sampling instruments.